两相流电阻层析成像测量电路与图像重建

提出一种用于两相流测量的高速电阻层析成像（electrical resistance tomography,ERT）系统。该系统采用双极性脉冲电流源为激励电极对提供激励信号,避免了直流激励造成的电极极化效应,同时简化了滤波电路的设计,相对于常规的交流激励ERT系统显著提高了数据采集速度。针对成像速度较快但成像质量差的线性反投影算法（linear back projection,LBP）,采用离线预迭代技术对其进行改进,提出一种改进型线性反投影算法（modified LBP, MLBP）,可高速重建较好质量的ERT图像。数值仿真和采用实际测量数据重建图像的结果表明,基于高速数据采集技术和改进的图像重建算法的高速ERT系统可实现两相流实时在线测量。     

Flow distribution and velocity measurement in a radial flow fixed bed reactor using electrical resistance tomography

Electrical resistance tomography is a relatively simple and inexpensive technique for imaging electrically conducting systems. It has been applied to visualise the flow pattern and distribution inside a radial flow packed bed of novel design for improving reactor performance with lower pressure drop. The density of information yielded by electrical tomography is suitable for validation of Computational fluid dynamics. Sets of tomographic images representing slices through a packed bed have been obtained for a 8-plane × 16-electrode sensor configuration which produces of the order 10³ conductivity measurements in three-dimensions. Pulse injections of high conductivity tracer, both uniformly in the feed and localised, can be imaged as multiple tomographic images or 3D solid-body images, revealing the internal flow pattern. Differentiation of the motion of the tracer peak conductivity within pixels in the sensing planes and between the planes allows the local flow velocities and directions to be determined. This quantifies the flow pattern for uniformity and radial distributive properties.     

PX氧化反应器中水含量的影响因素和软测量

建立了PX氧化反应器的数学模型,模型能够较好地预测不同工艺条件下的水浓度。基于上述模型,对现有工艺过程进行了数值模拟,发现含水量与反应温度和单位液相体积耗氧速率具有很强的相关性。通过数据回归得到了含水量软测量模型,上述模型为现有PX氧化过程的含水量实时控制提供了理论依据。     

热电阻测温与抗干扰问题的处理

水泥行业目前普遍采用DCS分布式集散型计算机控制系统,具有很强的适用性和较高的可靠性,通过软件编程即可实现工艺参数的监测与控制,使水泥生产过程实现自动化控制。由于DCS系统硬件配置功能较大,对来自水泥生产现场一次检测仪表的诸如Pt100热电阻测温信号、K型热电偶测温mV信号、脉冲开关量及标准电压电流信号均能直接进行信号处理,但有一个不容忽视的问题,如果来自现场的工艺参数测量信号在传输过程中混进干扰信号,DCS系统自身将很难抑制,需要在外部采取有效的措施给以解决。本文介绍Pt100热电阻测温信号异常引起故障的处理方法。     

Cholesterol and total fat content in farm-raised channel catfish cultured in North Carolina

Six batches of channel catfish, obtained from six different farms in North Carolina, were analyzed for lipid and cholesterol content. A total of 70 catfish were studied by high-performance liquid chromatography for cholesterol estimation. The mean cholesterol value was 33.00 mg/100 g of edible fish portion. The mean fat content was 4.93 g/100 g of sample. Cholesterol content increased with fat, and fat increased with weight, whereas moisture decreased with increasing fat.     

Effect of sintering temperature on the electrical and gas sensing properties of tin oxide powders

Tin oxide is an n-type semiconducting material having superior properties that can be utilized in several applications. The warning and detection of several dangerous gases in the environment are possible by utilizing gas sensors. The comprehensive functionality of these sensors could help to reduce the risk of severe health hazards and unexpected explosion risks. Tin oxide-based gas sensors exhibit reliable gas sensing performances along with respectful sensitivity and selectivity. Tin oxides in micro-and nano-particle forms provide an extremely high surface-to-volume ratio, which is favorable for gas sensors. Processing and synthesis of tin oxide particles accompany high-temperature processes, and this paper focuses on studying the effect of sintering temperatures on the structural and grain size of the commercially available tin oxide particles. The surface morphology of the tin oxide samples sintered at three different temperatures of 1100, 1200, 1300 ^°C shows a clear difference in the grain size and further affecting the dielectric properties of the materials. The gas sensing performances of three tin oxide samples are investigated by fabricating a pellet-type gas sensor. The sensor with the sintering temperature of 1200 ^°C exhibits the best gas-sensing performance with high response and low limit of detection (LOD). Our results suggest that the sintering temperature plays a vital role in deciding the dielectric properties and grain sizes, which are important parameters that affect the gas sensing behavior of tin oxide micro-and nano-particles.     

基于ECT和蚂蚁算法的油气两相流空隙率在线测量

基于电容层析成像系统（ECT）和蚂蚁算法,提出了一种油气两相流空隙率在线测量的新方法。该方法利用电容层析成像系统12电极电容传感器所获取的66个测量电容信息,首先根据电容层析成像系统所获取的流型辨识结果确定对应流型下的实际空隙率测量模型参数f和b,然后利用蚂蚁算法的信息素信息,找到当前测量状态下对空隙率起主要作用的组合电容集合和相应的权重系数,从而实现空隙率测量。与流型相对应的空隙率测量线性模型参数f和b基于先验数据通过最小二乘方法确定。油气两相流的实验结果表明,该方法对空隙率的在线测量是有效的,避免了复杂的图像重建计算,实时性能佳,测量时间小于0.08 s。在几种典型流型下,提出的空隙率测量方法与常用的快关阀方法相比最大测量偏差小于5.5%。     

Improving electrical conductivity and wear resistance of hafnium nitride films via tantalum incorporation

Transition metal nitrides are being widely applied, as durable sensors, semiconductor and superconductor devices, their electrical conductivity and wear resistance having a significant influence on these applications. However, there are few reports about how to improve above properties. In this paper, tantalum was incorporated into hafnium nitride films through Hf_1-xTa_xN_y [x=Ta/(Hf+Ta), y=N/(Hf+Ta)] solid solution. The electrical conductivity and wear resistance of the films were significantly improved, due to the increase of the electron concentration (tantalum has one more valence electron than hafnium) and the increase in H/E and H³/E² ratios caused by the effect of solid solution hardening, respectively. The highest electrical conductivity of Hf_1-xTa_xN_y films is 8.3×10⁵ S m⁻¹, which is 1.7 times and 5.2 times of that of hafnium nitride and tantalum nitride films, respectively. In addition, the lowest wear rate of films is 1.2×10⁻⁶ mm³/N m, which is only 10% and 48% of that of hafnium nitride and tantalum nitride films, respectively. These results indicate that alloying with another transition metal is an effective method to improve electrical conductivity and wear resistance of transition metal nitrides.     

Electric polarization and depolarization in cement-based materials, studied by apparent electrical resistance measurement

Electric polarization in cement-based materials (without conductive admixture) under an applied DC electric field was found by apparent electrical resistance measurement to be faster than subsequent depolarization under a reverse field by a factor ranging from 5 to 8. The slow depolarization suggested a degree of ionic trapping. In contrast, depolarization was even faster than polarization in carbon fiber cement, due to the fast hole response. Sand addition slowed down polarization saturation, but enhanced the polarization. Silica fume addition did not slow down polarization saturation, but diminished the polarization slightly. An increase in temperature enhanced the polarization due to increase in ionic mobility.     

Non‐ionic soft materials influence on filtration resistance and cake dry matter content

Filtration of organic slurries is important in many industries but challenging because the hydraulic resistance is high due to gel materials in the slurries. Particles with solid polystyrene (PS) core and varying amount of poly(N‐isopropylacrylamide) (PNIPAM) gel surface were synthesized. At low amount of gel, the gel deformed and partly filled the cake void increasing the resistance. This was successfully fitted using a semi‐theoretical model for deformable particles. At high amount of gel, the gel deformed filling the entire cake void and the resistance was dominated by the gel. During consolidation, the primary retardation time increased three orders of magnitude with gel thickness as expected as primary consolidation were dominated by the dissipation of pore water. The secondary retardation time also increased but not as pronounced as primary retardation time. Secondary consolidation was due to local compression of the gel and therefore less dependent on gel thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2241–2247, 2017     

Self-sensing of flexural strain and damage in carbon fiber polymer-matrix composite by electrical resistance measurement

The self-sensing of flexural strain and damage has been demonstrated in carbon fiber polymer-matrix composite by measuring the DC electrical resistance. Upon strain in the elastic regime, the compression surface resistance decreases reversibly (due to increase in the current penetration), while the tension surface resistance increases reversibly (due to decrease in the current penetration), and the oblique resistance increases reversibly. Upon minor damage, (i) the oblique resistance after unloading decreases, (ii) the oblique resistance decreases during load increase near the start of loading, and (iii) the curve of the oblique resistance or the resistance of the tension or compression surface vs. deflection becomes nonlinear. Upon major damage, all resistances abruptly and irreversibly increase, such that the onset occurs earlier for the compression surface resistance and the oblique resistance than the tension surface resistance. The surface resistances are superior indicators of strain, whereas the oblique resistance is a superior indicator of damage.     

Toward nanograined gadolinia doped ceria via two-step sintering at ultralow temperature and its electrical conductivity

Highly dense (>98%) and nanograined (∼60 nm) gadolinia doped ceria are obtained from ultrafine powders by adopting two-step sintering (TSS) procedure at an ultralow temperature of 750 °C with a dwell time of 20 h, which is the lowest sintering temperature for ceria family without sintering aids up to now. Electrochemical impedance spectroscopy investigations suggest that the electrical conductivities of densified electrolytes are closely related to sintering temperature and grain size, and GDC900-750 exhibits the highest total electrical conductivity of 3.640 S m⁻¹ at 700 °C in air. Fitting calculation indicates partial grain-size dependence of oxygen vacancy association enthalpy and grain-size independence of oxygen ion migration enthalpy. Grain boundary maturity influences on grain boundary conductivity to some extent, and younger grain boundary endues the densified electrolytes with higher grain boundary conductivity.     

Study of the swirling flow field induced by guide vanes using electrical resistance tomography and numerical simulations

In this work, the swirling flow field induced by guide vanes was studied using electrical resistance tomography (ERT) and numerical simulations. The results show that the two-phase water and oil mixture moves in the same axial direction for this type of flow field, which is very unlike the flow behavior of a traditional hydrocyclone with a tangential inlet. In the pipe behind the guide vanes, the smallest axial velocity and tangential velocity are located at the center of the pipe. From the pipe center to the pipe wall, both pressure and velocity increase gradually. Downstream of guide vanes, the maximal oil volume fraction is observed at the center of the pipe. From the center of the pipe to the inner wall, the oil volume fraction gradually decreases. Moreover, ERT can precisely show the oil distribution in the pipe section. These studies prove the possibility of efficient oil and water mixture separation by guide vanes, and the results may be very important for guiding the optimal design of vane-type pipe separators.     

Monitoring stability of reaction and dispersion states in a suspension polymerization reactor using electrical resistance tomography measurements

A system was constructed for visualizing the dispersion states of liquid monomer and polymer droplets in a suspension polymerization reaction in a non-intrusive and continuous manner using electrical resistance tomography measurements.Using this system, a method was established for keeping reaction states stable and the quality of the particles produced good by varying the mixing conditions, such as the rotational speed of the impeller and the injection amount of dispersion reagents, under the principles that the lower the rotational speed of the impeller, the better; and the smaller the injection amount of dispersing agents, the better.It was found that the amount of additional injection significantly affected both the sharpness and the average value of the particle diameter distribution, based on the data of the tomograms.     

A multi‐point electrical resistance measurement system for characterization of foam drainage regime and stability

Foam drainage regimes are significantly associated with the nature of the hydrodynamic resistance in foam structure. A multi‐point electrical resistance measurement technique has been applied for characterization of the drainage regimes and quantifying stability within standing foams. The capacity of the technique was confirmed by the estimation of macroscopic drainage rates for aqueous foams stabilized with sodium dodecyl sulfate. The drainage of sodium dodecylbenzenesulfonate, a commercial form of linear alkylbenzene sulfonate that is the most frequently used in household detergents was studied in detail by two complementary methods (forced and free drainage). The experimental data could be fitted using a power‐law with an exponent of 1/3 for forced drainage and of 1.0 for free drainage. These data indicate the following drainage behavior: mobile bubble surfaces, causing plug‐like flow within Plateau borders, thus dissipation mainly occurs inside the nodes. This research introduced an accurate method for quantifying foam stability that can be assessed by variations of real‐time measured foam heights that incorporate the evolution of the liquid content. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3143–3150, 2014     

Glass transition and melting behavior of carbon fiber reinforced thermoplastic composite,studied by electrical resistance measurement

DC electrical resistance measurement was applied to investigate the glass transition and melting behavior of carbon fiber reinforced nylon‐6 composite. The electrical resistance exhibited temperature dependencies that were attributed to the matrix molecular movements associated with structural transitions. The electrical resistance was affected by the degree of crystallinity and the thermal oxidative degradation, which were governed by the thermal history. The resistance results are consistent with differential scanning calorimetry (DSC) results. The resistance is more sensitive to the glass transition than DSC.     

Effect of outlet drying temperature and milk fat content on the physicochemical characteristics of spray-dried camel milk powder

Abstract

A composite face-centered experimental design was used to investigate the influence of spray drying conditions on the physicochemical characteristics of camel and cow milk powders. Response surface methodology (RSM) was deployed to appraise the effects of these processing parameters (the outlet drying temperature and the milk fat content) on water activity (a_w), glass transition temperature (T_g), bulk density, and free fat quantity. According to RSM analysis, it was noticed that the a_w and the T_g were primarily influenced by the outlet drying temperature instead of by milk fat content. Our results highlighted the negative effects of milk fat content and of the outlet drying temperature on the bulk density as well as on the free fat quantity of camel milk powder. Likewise, our findings underlined the negative effect of the outlet drying temperature on the bulk density of cow milk powder. However, the increase of fat content has led to the overexposure of fat at the free surface of the cow milk powder. Our results suggested a marked similarity of the overall thermodynamic behavior of both milks, during drying. Nevertheless, some differences were highlighted regarding the structuring of the particles of camel milk powder.     

Analysis of gas holdup in bubble columns with non-Newtonian fluid using electrical resistance tomography and dynamic gas disengagement technique

This paper presents an experimental analysis of the influence of the liquid rheology on the gas flow pattern in a bubble column reactor. Aqueous solutions of xanthan are selected as an example of non-Newtonian shear thinning fluid. Averaged gas holdup is determined by two experimental techniques: parietal pressure probes and electrical resistance tomography (ERT). ERT is also used to provide 2D images of the gas phase distribution in a column cross-section. Bubble size distributions are evaluated by a gas disengagement technique using the parietal pressure probes. All these techniques clearly show the gas flow pattern is different in Newtonian and non-Newtonian fluids. Gas holdup values decrease when increasing the liquid viscosity and reach a minimum or a plateau. Homogeneous flow regime, observed in water at low gas velocities, tends to disappear when viscosity increases. This evolution is visualized by a much less isotropic distribution of the gas phase within cross-section of the column and by the appearance of much larger bubbles due to an increased coalescence phenomenon.